步骤7：模板¶
现在是时候创建模板了。As you may have noticed, if you make requests with the app running, you will get an exception that Flask cannot find the templates. 模板使用Jinja2语法并默认开启自动转义。This means that unless you mark a value in the code with Markup or with the |safe filter in the template, Jinja2 will ensure that special characters such as < or > are escaped with their XML equivalents.
We are also using template inheritance which makes it possible to reuse the layout of the website in all pages.
将下面的模板放在templates文件夹里：
layout.html¶
This template contains the HTML skeleton, the header and a link to log in (or log out if the user was already logged in). It also displays the flashed messages if there are any. {% block body %}块可以被子模板中相同名字的块（body）替换。
session字典在模板中也是可用的，你可以用它来检查用户是否已登入。注意，在Jinja中你可以访问不存在的对象/字典属性或成员，比如下面的代码， 即便'logged_in'键不存在，仍然可以正常工作：
<!doctype html>
<title>Flaskr</title>
<link rel=stylesheet type=text/css href="{{ url_for('static', filename='style.css') }}">
<div class=page>
<h1>Flaskr</h1>
<div class=metanav>
{% if not session.logged_in %}
<a href="{{ url_for('login') }}">log in</a>
{% else %}
<a href="{{ url_for('logout') }}">log out</a>
{% endif %}
</div>
{% for message in get_flashed_messages() %}
<div class=flash>{{ message }}</div>
{% endfor %}
{% block body %}{% endblock %}
</div>
show_entries.html¶
这个模板继承了上面的layout.html模板来显示消息。注意for循环会遍历并输出所有render_template()函数传入的消息。注意，表单被配置成提交信息到add_entry视图函数，并使用HTTP的POST方法：
{% extends "layout.html" %}
{% block body %}
{% if session.logged_in %}
<form action="{{ url_for('add_entry') }}" method=post class=add-entry>
<dl>
<dt>Title:
<dd><input type=text size=30 name=title>
<dt>Text:
<dd><textarea name=text rows=5 cols=40></textarea>
<dd><input type=submit value=Share>
</dl>
</form>
{% endif %}
<ul class=entries>
{% for entry in entries %}
<li><h2>{{ entry.title }}</h2>{{ entry.text|safe }}
{% else %}
<li><em>Unbelievable. No entries here so far</em>
{% endfor %}
</ul>
{% endblock %}
login.html¶
This is the login template, which basically just displays a form to allow the user to login:
{% extends "layout.html" %}
{% block body %}
<h2>Login</h2>
{% if error %}<p class=error><strong>Error:</strong> {{ error }}{% endif %}
<form action="{{ url_for('login') }}" method=post>
<dl>
<dt>Username:
<dd><input type=text name=username>
<dt>Password:
<dd><input type=password name=password>
<dd><input type=submit value=Login>
</dl>
</form>
{% endblock %}
继续步骤8：添加样式 。